Molecular Dynamics Simulations, Solvatochromic Parameters, and Preferential Solvation in Aqueous Solutions of Ethaline, Ethylene Glycol, and Choline Chloride

Deep eutectic solvents (DESs) are recent solvents that have the basic characteristics close to ionic liquids, and they have been applied in several reactions. Adding molecular solvents especially water to DESs is beneficial in some cases such as biophysics and biochemistry. Therefore, understanding the effect of different solvents and preferred solvent is critical in binary mixtures. This work describes the principles to investigate the preferential solvation of probe dyes (4-nitroaniline, 4-nitroanisole, and Reichardts dye 30) in complex mixed solvents in detail. Experimental and theoretical studies were used to seek the preferential solvation of probes in aqueous solution of ethylene glycolcholine chloride (ethaline) and its components (aqueous solutions of ethylene glycol and choline chloride). Results confirmed that probes prefer to be solvated by ethaline and ethylene glycol. In detail, the microsphere solvation of probe dyes was analyzed, which confirmed fundamental roles of choline and ethylene glycol for synergism effects from ideal mixtures. In most of the mole fractions, probes prefer to be solvated in the order of components, namely, ethylene glycol and choline > water > chloride. Moreover, aggregation of solvents components around probes was calculated profoundly. Molecular dynamics simulations made it possible to understand which combinations of components in mixed solvents display preferential solvation. Also, as a minor goal, solvatochromic parameters in mentioned mixtures were discussed in the related section. Finally, density functional theory (DFT) calculations showed either bathochromic or hypsochromic shifts coming from changes in microsphere solvation and hydrogen bonding of probes with solvents.